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Basic Concepts of Chemistry Online Mcqs Test

Maan AliLast Updated: October 14, 2025

Important Basic Concepts of Chemistry Question and Answer

Total Questions:	71
Time Allowed:	30 Minutes
Total Marks:	71
How to Attempt Test:	Please choose the right Option in MCQ-type question.
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Basic Concepts of Chemistry Practice Test Online With Explanation

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Page 1 of 3

1. The percentage of oxygen in NaOH is

2. Calculate the number of moles of CaCO₃ (Formula weight = 100) in a sample that weighs 25.0 grams.

1.00

0.5

0.75

0.25

3. Which of the following statements is wrong about isotopes?

They possess different mass number

They possess same position in the periodic table

They possess same chemical properties

They possess same physical properties

4. Indicate the incorrect statement form the following

The empirical and molecular formula of some of the compounds are same

Stoichiometric calculation can only be done if no side reaction happen

A limiting reactant is used at the end of reaction

Actual yield is always less than theoretical yield

5. The prefix 10¹⁸ is

Kilo

Nano

Giga

Exa

6. Irrespective of the source, pure sample of water always yields 88.89% mass of oxygen and 11.11% mass of hydrogen. This is explained by the law of

Multiple proportions

Constant volume

Conservation of mass

Definite proportions

7. The hydrogen phosphate of certain metal has formula MHPO₄. The formula of metal chloride would be

MCL₂

MC1₃

MC1

M₂C1₂

8. How many moles of Helium gas occupy 22.4 L at 0°C at 1 atm. Pressure?

0.90

0.11

1.11

1.0

9. Which law directly explains the law of conservation of mass?

Newton’s law

Hund’s rule

Dalton’s law

Moley’s law

10. A ring contains 1.2g of diamond. How many number of carbon atoms are in diamond?

6.02 x 10²²

6.02 x 10²³

3.01 x 10²³

3.01 x 10²²

11. Isotopes differ in the

Number of neutrons

Number of electrons

Number of protons

Number of atoms

12. An oxide of nitrogen contain 36.8% nitrogen and 63.2% oxygen by mass. Calculate its empirical formula.

N₂O

N₂O₃

NO₂

13. One of the substances is used to absorb CO₂ gas in combustion analysis. Which is that substance?

SiO₂

Al₂O₃

Mg(ClO₄)₂

KOH

14. How can you separate the mixture of two gases of different atomic masses?

Graham’s Law of diffusion

Chromatography

Sublimation

Crystallization

15. Most atoms are neutral, to become a positive ion the atom must:

None of these

Lose electrons

Gain electrons and protons

Lose electrons and protons

16. Which of the following is a pure substance made up of two or more types of atoms or elements?

Mixture

Crystal

Element

Compound

17. How do you calculate the number of neutrons in an atom?

The atomic mass subtracted the number of protons

The atomic mass plus the number of protons

The atomic mass plus the number of electrons

The atomic mass subtracted the number of electrons

18. Empirical formula of chloroform is

CHCl₃

CH₃cl

CH₂C₁₂

CHCl

19. The volume occupied by 28 gram of N₂ at STP?

1.12 dm³

22.4 dm³

2.24 dm³

112 Cm³

20. The compound having highest percent of oxygen is

C₂H₅OH

CH₃COOH

H₂O

CH₃COCH₃

21. Percent of calcium in calcium carbonate is

20%

80%

30%

40%

22. What do you call pure substances that are formed from the attraction between positive ions and negative ions?

Ionic charges

Ionic element

Ionic atoms

Ionic compounds

23. What is a multivalent ion?

Some ions can have only one charge

Only negatively charged

An ion that can have more than one charge

Ions that are made of more than one type of atom and act as one

24. A compound contains 6.0 g of carbon and 1.0 g of hydrogen. The percent composition of the compound is:

17% hydrogen and 83% carbon

14% hydrogen and 86% carbon

86% hydrogen and 14% carbon

83% hydrogen and 17% carbon

25. Which of the following is an element?

Common Salt

Gold

Water

Sugar

Page 2 of 3

26. The Number of oxygen atoms in 4.4 g of CO2 is approximately

1.2 x 10²³

6 x 10²²

12 x 10²³

27. What is the percent water in hydrated calcium chloride (CaC1₂ 2H₂O)?

12.26%

32.47%

24.51%

66.67%

28. What is correct relationship between empirical and molecular formulas?

Empirical formula x √n = Molecular formula

Empirical formula x n² = Molecular formula

Empirical formula /n = Molecular formula

Molecular formula /n = Empirical formula

29. Diameter of an atom is in the range of

0.2 m

0.2 nm

2 x10¯¹⁰

0.2 Pm

30. Which of the following represents an element?

A pure substance made up of one type of atom

A compound made up of one type of element

The periodic table

A pure substance made up of two or more types of atoms

31. Which of the following is NOT true of matter on the Earth?

Matter is always composed of atoms

All substances are made of matter

All matter contains chemical elements

Matter always consists of molecules

32. The modern atomic weight scale is based on

H¹

C¹³

O¹⁶

C¹²

33. An anhydrous salt of copper is found to contain 52.7% chlorine and 47.3% copper by mass. What is the empirical formula for this salt?

CuCl₂

Cu₂Cl₃

CuCl

CuCl₃

34. What does the atomic number of an atom represent?

Electrons and shells

Neutrons and electrons

Protons and electrons

Protons and neutrons

35. Calculate the weight, in grams, of one molecule of carbon dioxide, CO₂.

1.99 x 10¯²³

7.31 x 10¯²³

4.65 x 10¯²³

1.37 x 10²²

36. Which of the following is NOT a pure substance?

Gold

Sodium Chloride

Soil

Water

37. How many elements are present in two molecules of aspirin? The formula for aspirin is C₉H₈O₄.

38. How many moles of KBrO₃ are required to prepare 0.0700 moles of Br₂ according to the reaction: KBrO₃ + 5KBr + 6HNO₃ → 6KNO₃ + 3Br₂ + 3H₂O

0.210

0.0233

0.0732

0.0704

39. What is a chemical compound?

A subatomic particle

A combination of two protons and two electrons

A mixture of two or more substance

A combination of two or more chemical elements

40. Which of the following statements is FALSE for the chemical equation given below in which nitrogen gas reacts with hydrogen gas to form ammonia gas assuming the reaction goes to completion?
N₂ + 3H₂ → 2NH₃

The reaction of three moles of hydrogen gas will produce 17 g of ammonia

The reaction of one mole of H₂ will produce 2/3 moles of NH₃.

One molecule of nitrogen requires three molecules of hydrogen for complete reaction.

One moles of N₂ will produce two moles of NH₃.

41. What are the two different types of ions?

Negative and positive

Polyatomic and multivalent

Electrons and protons

Polyatomic and compound ions

42. The empirical formula of a compound is CH₂O and its molecular mass is 120. The molecular formula of the compound is

C₃H₆O₃

C₂H₄O₂

C₄H₈O₄

CH₂O

43. Which of the following method is used to estimate oxygen in an organic compound?

Combustion method

Duma’s method

K. Jeldahl’s method

All of above

44. Which of the following could be an empirical formula?

C₆H₁₂O₆

H₂O₂

BaO₂

C₂H₄

45. Molecular compounds can be found in all three states of matter at room temperature. Which molecule compound is a liquid at room temperature?

Carbon dioxide

Water

Methane

Sugar

46. The set of numerical coefficients that balances the chemical equation K₂CrO₄ + CH1 → K₂Cr₂O₇ + KC1 + H₂O

2, 1, 1, 2, 1

2, 2, 1, 1, 1

1, 1, 2, 2, 1

2, 2, 1, 2, 1

47. A gaseous mixture contains 50% helium and 50% methane by volume. What is the percent by weight of methane in the mixture?

50%

80.03%

20.05%

19.97%

48. What is the net charge on ferrous ion?

49. The empirical formula of the compound having 50% sulphur and 50% oxygen by mass is

SO₃

S₂O₃

SO₂

50. Ayesha required an aqueous solution of sodium chloride. She made the solution by dissolving salt in:

Water

Vinegar

Air

Oxygen gas

Page 3 of 3

51. How will you separate a mixture of two gases?

Osmosis

Graham’s law of diffusion technique

Fractional distillation technique

Chromatography

52. To differentiate between C-12, C-13 and C-14, the instrument that you would use is

Infra-red spectrometer

Atomic absorption spectrometer

Mass spectrometer

Ultraviolet spectrometer

53. Since atoms are neutral, the number of electrons is equal to the number of:

Protons

Ions

Neutrons

Nucleus

54. Balance the following equation using minimum integral coefficients: (NH₃ + O₂ → NO₂ + H₂O) Find the stoichiometric coefficient for oxygen gas O₂:

55. If the empirical formula of compound is CH₂. Which of the following is true about its molecular formula?

Only one molecular formula (C2H2) is possible

Its molecular formula does not exist

Only one molecular formula (CH2) is possible

More than one could be a molecular formula for CH₂

56. Vapor density of a gas is 22. What is its molecular mass?

57. Which one of the following is ambiguous?

A mole of hydrogen

A mole of sodium atoms

A mole of electrons

A mole of potassium ions

58. Among the following pairs, the one which illustrates the law of multiple proportions is

CS₂, FeSO₄

H₂S, SO₂

NH₃, HC1

CuO, Cu₂O

59. Difference in density is the basis of

Molecular attraction

Molecular sieving

Gravity separation

Ultrafiltration

60. Water (H₂O) is a common compound made up of:

3 elements and a total of 2 atoms

2 elements and a total of 2 atoms

3 elements and a total of 3 atoms

2 elements and a total of 3 atoms

61. Copper (II) oxide is mixed with organic compound during combustion. The purpose is

To reduce the time for completion of the reaction

All of these

To carry out compete combustion

To reduce the economy of the process

62. If Na is Avogadro’s number, then number of valence electrons in 4.2 g of nitride ions N³¯ is

1.6 Na

2.4 Na

4.2 Na

3.2 Na

63. Bromine has two isotopes having the relative abundances as ⁷⁵₃₉Br = 50.51% and ⁸¹₃₅Br= 49.49%. The average atomic mass of bromine is

79.5

64. For which of the following terms empirical formula cannot be applied?

H₂O

NaC1

CC1₄

It can be applied to all

65. How many moles of CO₂ are present in 220 mg?

5 moles

10 moles

5000 mole

0.005 mole

66. What are the parts of an atom?

Protons, neutrons, nucleus, mass

Nucleus, element, carbon, space

Protons, neutrons, electrons, nucleus

Ions, electrons, neutrons, water

67. The coefficient of viscosity η of a fluid moving steadily between two surfaces is given by the formula, f = η dV/dx where f is the frictional force on the fluid. A is an area in the fluid and dV/dx is the velocity gradient inside the fluid at that area. The S.I. unit of viscosity coefficient η is given as,

Newton

Nil, it is dimensionless constant

Nm¯²s¯²

Kg m¯¹s¯¹

68. Which of the following represents a compound?

Pure substances made up to of 2 or more types of atoms

Two words in one word

Made up of 10 atoms

A pure substance made up of one type of atom

69. How many number of ions are there in 98 grams of sulphate ions?

4 x 6.02 x 10²³

3 x 6.02 x 10²³

6.02 x 10²³

6.02 x 10²³ x 2

70. 1 mole of CH₄ contains

4 g-atom of hydrogen

3.0 g of carbon

1.81 x 10²³ molecules of CH₄

6.02 x 10²³ atoms of H

71. What are the ratios among the volumes of gases of ³²O₂,²H₂, and ¹⁶CH₄ if equal mass of each gas is taken?

1:16:2

2:16:1

2:16:2

1:1:1

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Maan AliLast Updated: October 14, 2025

33 Comments

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October 26, 2022 at 2:22 pm

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October 26, 2022 at 1:52 pm

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October 12, 2020 at 4:43 pm

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Momo says:

December 9, 2018 at 11:24 am

Mass of one mole of iodine is 254g not 245g. (127*2=254g)

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Basic Concepts of Chemistry Online Mcqs Test

Important Basic Concepts of Chemistry Question and Answer

Basic Concepts of Chemistry Practice Test Online With Explanation

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